Oil cracking process



Nov. 8, 1938.

G. c. PECKHAM OIL CRACKING PROCESS Filed April 27, 1955 '2 sheets-sheet 1 'lll NF bw Nov. 8, 1938.

G. c. PECKH'AM OIL CRACKING PROCESS Filed April 27, 1955 2 Sheets-Sheet 2 George Patented ov.,

STATES PATENT oFFici-z Application April 21,

dlalms.

This invention deals generally with the cracking of petroleum oils, and relates more particularly to systems in which the oil is cracked by direct contact with a suitable molten metal or inorganic salt heated to cracking temperatures. In some of its aspects, the invention may be regarded as an improvement in the general type of cracking process described in a copending application,

Ser. No. 637,116, filed by Wayne A. S. Harmon l0 on Process for cracking hydrocarbons.

The present process may be broadly characterized as an oil cracking system in which preheated liquid oil, or oil vapors, or both, are injected into a stream of molten metal being circulated at a fairly rapid and uniform rate of iiow by a suitable mechanical means, such as a `rotary pump. 'Ihe molten metal is maintained in a circuitous path of ow passing through a heating zone, wherein the temperature of the 20 metal is raised sulciently high to supply the heat necessary to crack the hydrocarbon, and thence in a continuous and uniform velocity stream vertically through the cracking zone. The hydrocarbon is cracked at a temperature sumciently high to reduce the residue to a dry and very finely divided carbon which rises to-the surface of the molten metal in the cracked zone and is continuously swept away in the cracking vapor stream into a separating chamber. The present 30 system differs in one important respect from the process described in the Harmon application referred to above in that the hydrocarbon and molten metal flow in the same upward direction within the cracking zone, whereas in the Harmon system the oil and metal streams ow countercurrently with the oil vapors rising through a down-flowing stream of molten metal.

One of my principal objects is to provide a process for cracking oil to a dry powdered car- 40 bon residue by direct contact with a stream of molten metal owing continuously under the infiuence of a mechanica and positive acting circulating means; also, to provide a process of this type that is particularly adaptable to flexibility.v

' and accuracy of control and to the maintenance of closely controlled cracking temperatures. Two of the principal features responsible for the accomplishment of this object are the circulation of the molten metal in a controllably uniform and constant rate of circulation, and the passage of the metal and hydrocarbon in the same upward direction within the cracking zone.

Experiments have shown that in order to obtain the most efficient oil conversion and to insure the continuous formation and removal of 1935, Serial No. 18,612

(Cl. ISG- 70) the desired residue, i. e., dry powdered carbon, certain heating and temperature conditions must be maintained in the cracking zone. In the first place, with the charging stock being continuously injected into the cracking zone, the amount of 5 heat required to crack the oil must be proportionate to the rate of feed and must be supplied at a correspondingly constant rate. The maximum temperature to which the vapors are heated must be suilciently high to reduce the residue l0 to dry carbon, but without substantial overheating that would result in the production of excessive amounts of xed gas. Since the molten metal stream is the medium by which heat is supplied to the oil undergoing cracking, it will be l5 seen that the amount and rate of heat supplied to the cracking zone, as well as the maintenance of particular temperature conditions therein, are del.` .denJ upon the rate of molten metal circulation; hence the necessity for maintaining the metal in a continuously moving stream and for controlling the rate of its flow is of primary importance.

By reason of the adaptability of the present system to absolute and accurate control of the amount and rate of molten metal circulation, I am able to control with corresponding accuracy the heating and temperature conditions 2.1.". the cracking zone and therefore the character and proportions of the products resulting from the cracking reaction. At the same time, I am able to insure the reduction of the residue to a fine carbon powder and to eifc-ctively remove carbon from the cracking zone to the extent that even after long periods of operation, the cracking chamber will remain free from any substantial accumulations oi carbon.

Other objects of the invention are directed to the provision of a system capable of producing abnormally large percentage yields of cracking gasoline possessing high anti-knock or octane rating, and a minimum of sulphur and other corrosive bodies. The cracked gasoline product is further characterized by the unusually small amounts of acids or clays required for its treatment to nished gasoline. Various features of the invention contribute to the accomplishment of these general objects, and while all such features might at this point be preliminarily referred to and discussed, it is believed that a better and more ready understanding of the entire invention can be given by proceeding directly with a description of one illustrative form thereof.. For purposes of description, reference is had to the accompanying drawings, in which:

Fig. 1 is a general diagrammatic view showing a preferred form of oil cracking system embodying the invention;

Fig. 2 is a fragmentary enlarged section taken on line 2--2 of Fig. 1; and

Fig. 3 is an enlarged fragmentary view, showing the upper portion of the oil cracking chamber.

Referring first to Fig. 1, the retort wall structure, generally denoted by the reference numeral I0. encloses a series of heating chambers which may be individually red or heated by combustion gas circulation from a primary heating chamber II equipped with burners I2. A closed heating chamber I2a containing a molten metal circulating pump I3, hereinafter referred to more in detail, communicates with chamber I I through opening I4. The main combustion gas stream leaving chamber II passes through opening I5 into chamber I6, through which the hot gases ilow upwardly along the shell I1 and out through opening I8 into chamber I9 containing carbon trap 20. The gases then pass out through opening 2I into chamber 22 containing a comparatively large volume shell 23 which forms the later described gas conversion chamber.

The vertically positioned shell I1 forms an externally heated cracking chamber, and may conveniently comprise upper and lower cylindric sections I'la and Ilb of comparatively larger and smaller diameters, respectively. Oil is subjected to cracking in shell I1 by direct contact with a continuously circulated stream of molten metal 25, (see Fig. 3) typically and preferably molten lead. The molten metal is discharged through inlet line 2S into the lower portion of section I1b of the cracking chamber, and is then caused to flow upwardly through the cracking zone in a rapidly moving stream. As best illustrated in Fig. 3, the molten metal 25 flows laterally from section I1a of the cracking chamber through shell 21 into line 28 connecting with the section inlet 29 of pump I3.

Pump I3 is of the rotary impeller type, operating to circulate the molten metal in a nonpulsating, uniform velocity stream, and the pump structure is shown diagrammatically as comprisingv a body I3a containing an impeller 30 driven through shaft 3I by motor 32. In being contained substantially entirely, except for the motor, within chamber I 2a, the pump will be externally heated to a temperature sumciently high to avoid solidiflcation of any of the circulating metal within the pump. Molten metal ilowing upwardly within the pump body above the impeller is returned to the suction line 28 by way of drain pipe 33.

The molten metal is discharged by pump I3 through pipe 34 and heating coil 35 into the cracking chamber via inlet line 25. While being circulated through the heating coil 35, the metal stream is heated to a temperature suiciently high to maintain the hereinafter described cracking conditions within shell I1. By varying the operating speed of pump I3, the rate at which the molten metal is circulated, and the velocity of the metal stream flowing upwardly through the cracking chamber, may be closely adjusted to control the cracking operation by varying the time period during which the oil is maintained in contact with the metal stream. As illustrated in Fig. 2, the molten metal may be drained from the system through a valve line 36 extending through a bottom closure I1c positioned within shell I1b a short distance below the inlet 25.

Preferably, the oil charging stock is preheated and partially vaporized prior to being injected into the cracking zone, and while it is understood that the oil preheating operation may be carried out by any suitable method and apparatus, I have showna typical preheater 31 of the shell still type into which the charging stock is fed through line 38. The charging stock will be preheated in shell still 31 to a temperature ranging from say 400 to 550 F., under whatever back pressure is imposed by the cracking system. The unvaporized oil ilows from still 31 through line 39, and is discharged by pump 40 through line 4I and injection nozzle 42 into a suitable point within chamber I1b above the molten metal inlet 25.

The injection nozzle structure 42 has been specially designed with the view of preventing the charging stock from carbonizing and clogging the injection orice, by continuously circulating a stream of oil past the orifice and the injection valve, the oil temperature being kept suillciently low by continuous circulation to prevent carbonizing at the point of injection into the cracking zone. Referring to Fig. 2, the injection valve structure 42 comprises a body 43 welded or otherwise attached at 44 to the side of shell I1b, and having a discharge orifice 45 controlled by a needle valve 45 extending through a suitable stuiling box 41. Pipe 4I connects with a U- shaped passage 48 through an enlarged .portion 48a of which the needle valve 46 extends. The outlet side 48h of the passage connects with a return ilow line 48 leading back to shell still 31. T'he oil injection pressure within passage 48a of the injection nozzle is controlled by an ad` justable pressure regulating valve 58 in 1ine'43..

acting to maintain a predetermined back pressure against pump 4II. i

- In operation. a portion of the circulating oil stream, dependent on the oil pressure and the adjustment of needle valve 48, is discharged through oriiice 45 directly into the upwardly ilowing stream of molten metal within chamber I 1b. The remaining portion of the oil stream flowing through passage 48 is circulated across the valve controlled end of orifice 45 and in contact with the valve itself, and is circulated back through passage 48h and line 43 to the preheating still. Although the oil is preheated, its temperature will be below that at which appreciable cracking or carbonization will occur, and as a result of the continued circulation past the injection port and valve, the temperatures in the vicinity of the orlce will be kept suiliciently low to prevent the orifice and valve from collecting carbon to an extent'necessitating frequent shutdowns for cleaning.

Preferably the molten metal will be maintained in the cracking zone at a temperature suiliciently high to vaporize substantially all the volatile constituents of the oil, so that the immediate products of the cracking reaction will consist of cracked vapors and a more or less dry powdery carbon residuum. Under these conditions, the temperature of the molten metal within the cracking zone will range in the neighborhood of from 1000* to 1400 F., depending upon the nature of the charging stock. The injected oil and molten metal flow upwardly together within the cracking zone; the depth of the molten metal column, the rate of oil injection, and the velocity of the molten metal stream all being controllable and regulated to maintain the oil in contact with the molten metal for that period of time which, under the existent conditions, will most efficiently promote the cracking reaction to the desired extent.

The powdered carbon residue collects on the surface 52 of the metal stream and is continuously'removed in the stream of cracked vapors flowing from the cracking chamber. As the molten metal flows from chamber I1athrough shell 21 to the outlet line 28, the cracked oil vapors sweep across the surface 52 of the metal, picking up the powdered carbon residue, and carrying it out through lines 53 and 84 into carbon trap 20, wherein the carbon settles out into the base of the trap. The carbon'may be intermittently removed from the trap, or continuously asby means of an ejector 55 connecting with the carbon outlet pipe 55. In the event the upward cracked vapor of gas velocity through the surface of the molten metal in chamber 11a is suillciently high, the vapors and carbon residue may be discharged from the .top of the chamber through line 58 connecting with pipe 54, or, if desired, the cracked vapors may be discharged through both lines 53 and 58.

The preheated oil vapors passing from still 31 through lines 60 and 8l preferably are combined with the cracked oil vapors leaving the cracking chamber, although if for any reason it is found desirable to' treat the preheated oil vapors separately from the cracked vapors, the former may be passed through line 52 for condensation or anyother further treatment. For the purpose of combining the preheated and cracked oil vapors, the former may be conducted through lines 63 and 54 into the top of chamber I1a, or at any other suitable point in the cracked oil vapor stream leaving the molten metal 25, the combined vapors then flowing through lines 58 and 54 to the carbon trap 20. In order to assist the removal of the powdered carbon residue from the surface 52 of the metal stream, a portion or all of the preheated oil vapors may be passed through a liniev leading at 56 into shell 21, and terminating in an upwardly directed outlet 61 located a short distance below the molten metal surface 52. The vapors being discharged upwardly from the outlet 81, agitate the surface of the metal stream'and blow the carbon toward the cracked vapor outlet 53 and into the transversely flowing stream of cracked vapors. It is to be understood that while it is most convenient to utilize a portion or all of the preheated vapors as a gas 'for agitating and blowing the carbon residue from the surface of the metal stream in the manner explained, any suitable gas derived from. a source extraneous to the cracking chamber may be used for this purpose.

As a further alternative method of introducing the preheated Voil vapors into the cracking system, the vapors from the preheater may be passed through lines :88 and 69 into cracking chamber 11b ata suitable distance below the surface of the metal stream. 'I'he vapors then are subjected to cracking at the high temperatures existing within the cracking zone, and the resulting vapors combined with the cracked vapors produced from the preheatedA oil. Under the last mentioned mode of operatiorji', therefore, the charging stock is subjected to both liquid and vapor phase cracking within the same cracking zone. In view of the fact that the oil being introduced to the cracking zone through line 89 is already in vapor phase, it will ordinarily require less time in contact with the molten metal to effect the desired conversion. Consequently, the vapors will usually be introduced at a point 10 above the point of entry of the liquid oil stream to the cracking zone through line 28. It may be further mentioned that in addition to effecting both liquid and vapor phase cracking of the stock, the introduction of vapors through line 68 to the cracking chamber has the additional advantage of facilitating the removal of carbon residue from the surface of the metal stream by reason of the increased vapor 64, are provided for the purpose of preventing the molten metal in the cracking chamber from being forced back through pipes or 89 into the vapor lines.- If for any reason the pressure in vapor line 6I should drop to the extent that the vapor pressure in chamber 11a would tend to expel the molten metal through the vapor lines, the check valv will immediately seat and arrest surging of the metal.

In order that reformation of the cracked vaPOrs may be allowed to take place to the fullest possible extent within practical limitations, I preferably maintain the cracked vapors in an enlarged conversion chamber for a predetermined period of time, prior to preliminary condensation or fractionation. For this purpose, the vapors leaving carbon trap 20 'through lines 11 and 18 may be discharged into an enlarged conversion chamber 23 of such capacity that a time period of at least one or two minutes will be required for the vapors to iow through to the outlet 19. By thus holding the vapors in the chamber for a time interval, dissociation and reformation of the cracked hydrocarbons are allowed to approach completion while the oil is held in vvapor phase.

Back pressure valve in the conversion chamber outlet line 19 may be set to maintain any suitable back pressure on the entire system While ordinarily it will be preferred to crack the usual'methods and apparatus adatable for the' purpose. It may be mentioned that in case the conversion chamber 23 is used, carbon trap 20 may be dispensed with and the carbon residue separated from the cracked vapors within the conversion chamber itself. In this case, the carbon trap will be bypassed by a line 8l connecting pipes 53 and 58 with the conversion chamber inlet line 18.

In starting the system into operation and before the heat transferring metal 25 is put into the system, the apparatus may first be brought up to operating temperatures by passing superheated steam through the molten metal circulating system. The steam may be introduced at any suitable point, as by way of line 82 connecting with the molten metal pump discharge line 34. After operating temperatures have been reached, the heat conducting metal 25 may be introduced at any suitable point, as by way of pipe 83 in the top of cracking chamber 41a.

After all'the metal has been introduced and circulation established. the system is started into :operation by opening valve II and injecting the preheated charging stock into the cracking chamber. In shutting down the system, the oil and vapor linea leading to the cracking chamber are closed and the molten metal drained from mately 99% calculated on the basis of the vol-A ume of charging stock. The gasoline yield recoverable from the pressure distillateeither by redistillation of the latter or by fractionation of the cracked vapors, has been lfound to run as high as 88% of the charging stock volume. As previously observed, tests made upon gasoline refined in accordance with the invention have indicated octane ratings running as high as 86%, and have shown theproduct to be substantially free of sulphur and residual corrosive or gummy substances.

I claim: l

1. The method of cracking hydrocarbons that includes, pumping a stream of molten metal in a circuitous path of tlow through a heating zone and then through a cracking zone, preheating and partially vaporizing an oil charging stock, separating the vapors from the unvaporized oil, discharging the preheated oil directly into the molten metal within'the cracking zone, heating the oil during its contact with the molten metal to a temperature at which the oil is cracked and entirely vaporized, leaving a carbon powder residue on the surface or said metal stream, continuously removing said residue from the cracking molten metalwithinthe cracking zone, heating v the oil during-its'contact with themolten metal to a temperature at which the oil is cracked and entirely vaporized, leaving a carbon powder residue, on the surface of said metal stream, continuously removing said residue from the crackingzone in a stream of cracked oil vapors, and combining with said crackedvapors, oil vapors produced insaid preheating operatian` by introducing the last mentioned vapors. into the molten metal within the cracking zone. 'f

3. The method of cracking hydrocarbons that includes, maintaining a-.gbody'l of molten metal within a cracking zone, preheating and partially vaporizing an oil charsing stock, separating the vapors from the unvaporized oil, introducing, the preheated oil directlyfinto the molten metal within said cracking zone, heating the oil, during its contact with the molten'metal to a tem perature at which the oil is cracked and vaporized, leaving a residue on the surface of the metal stream, withdrawing cracked vapors and residue from the cracking zone, and introducing vapors from said oil preheating operation into the molten. metal within said cracking zone. 1:.

4. The method that includes, maintaining a body of molten metal within a cracking zone, preheating and partially vaporizing an oil cracking stock, separating the vapors from the unvaporized oil, introducing at least a portion ci the unvaporized preheated oil into said body ot molten metal, and separately introducing at least a portion of the vapors from the preheated oil into said body oi' molten metal.

Y GEORGE C. PECKHAM. 

